Capture, editing and encoding of motion pictures encoded with repeating fields or frames

ABSTRACT

An image sequence captured at a first image rate is encoded as an encoded image sequence at a second image rate with information in the encoded image sequence indicative of images that are repeated when decoded. To assist in editing a video program using the encoded image sequence, the information in the encoded image sequence indicative of repeated images may be cleared and image index information for the encoded image sequence generated to map a temporal position of an image in a decoded image sequence to a position of corresponding data in the encoded image sequence. Temporal positions used with the image index information correspond to the first image rate. Editing video involves defining a sequence of clips that reference source encoded image sequences using edit points. Each clip has a start and end point in its corresponding source and a position in the edited video program. The temporal resolution of these edit points corresponds to the first image rate. An edited video program may be output as an encoded image sequence, using the source encoded image sequences referenced by the sequence of clips. The encoded image sequence is constructed according to the edited sequence of clips, using the source encoded image sequences.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of, under 35 U.S.C.§120, and is a divisional application of pending application Ser. No.11/363,718, filed Feb. 28, 2006, which is a nonprovisional applicationclaiming priority under 35 USC §119 to provisional Application Ser. No.60/671,629, filed Apr. 15, 2005, abandoned, both of which areincorporated herein by reference.

BACKGROUND

There are several formats currently available for encoding motionpictures, i.e., a temporal sequence of images. Some of these formats arestandards and include, but are not limited to, the standards commonlyknown as MPEG-2 (formally known as ISO/IEC 138182 or ITU-T Rec. H.262)and H.264 (formally known as ISO/IEC 14496-10 or ITU-T Rec. H.264).Other formats may borrow concepts from or use parts of these standards.For example, a format known as HDV encodes a progressively scannedhigh-definition image sequence captured at a rate of 23.976 frames persecond using MPEG-2 encoding. The captured image sequence is encoded asan image sequence at a second image rate, e.g., 29.97 frames per secondor 59.94 fields per second, with information in the encoded imagesequence indicative of fields or frames that are repeated when decoded.In MPEG-2, this information includes a value known as a “repeat firstfield flag.” In H.264 this information is provided by a variable called“pic_struct.”

It can be difficult to edit a video program using an image sequence thathas been encoded using repeated fields or frames. In particular, it isdifficult to maintain accurate timing relationships between sources ofimage sequences and the edited video program. Such timing requires aproper understanding and use of the information that indicates whether afield or frame is repeated in a wide variety of possible editingoperations.

SUMMARY

An image sequence captured at a first image rate is encoded as anencoded image sequence at a second image rate with information in theencoded image sequence indicative of images that are repeated whendecoded. To assist in editing a video program using the encoded imagesequence, the information in the encoded image sequence indicative ofimages that are repeated when decoded may be cleared. Further, imageindex information for the encoded image sequence may be generated. Thisimage index information is used to map a temporal position of an imagein a decoded image sequence to a position of corresponding data in theencoded image sequence. Temporal positions used with the image indexinformation correspond to the first image rate.

Editing a video program involves defining a sequence of clips thatreference source encoded image sequences using edit points. Each cliphas a start and stop point (which may be inferred from a duration) inits corresponding source and a position for the clip in the edited videoprogram. The temporal resolution of these edit points corresponds to thefirst image rate. The information in the encoded image sequenceindicative of images that are repeated when decoded may be ignored ormay have already been cleared. During editing, the edited video programmay be played back at the first image rate. To playback the edited videoprogram at another image rate, such as the second image rate, images maybe repeated. Whether an image is repeated depends on a cadence thatcorresponds to a difference between the first image rate and the otherimage rate and is independent of any information in the source encodedimage sequences that may indicative of images that are repeated whendecoded.

An edited video program may be output as an encoded image sequence,using the source encoded image sequences referenced by the sequence ofclips. The encoded image sequence is constructed according to the editedsequence of clips, using the source encoded image sequences. Inparticular, the encoder clears any information in the source encodedimage sequences indicative of images that are repeated when decoded. Inthe output encoded image sequence, information indicative of images thatare repeated when decoded is set according to a cadence associated witha difference between the first image rate and the second image rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is data flow diagram of an example system that captures, editsand encodes audio and video data.

FIG. 2 is data flow diagram illustrating processing of multiplexed,encoded audio and video data.

FIG. 3 is an illustration of an effect applied to encoded data.

FIG. 4 is a flowchart describing how to encode an edited sequence.

DETAILED DESCRIPTION

Referring now to FIG. 1, an example system 100 for the capture, editingand encoding of motion pictures will now be described. In this examplesystem, encoded data 102 from a source of audiovisual information (notshown), such as a camera, is received. The encoded data is encoded withrepeating images, whether fields or frames. Thus the encoded datarepresents an image sequence that was captured at a first image rate(such as 24/23.976 frames per second or 48/47.952 fields per second) andis encoded for playback at a second image rate (such as 25, 29.97 or 30frames per second or 50, 59.94 or 60 fields per second). A captureprocess 104, described in more detail below, processes the encoded data102 to product processed encoded data 106 that is stored in storage 108.An editing system 110, described in more detail below, with access tostorage 108 allows an operator to define a sequence 112 of clips of theprocessed encoded data 106. The edited sequence 112 is used by an exportprocess 116, described in more detail below, along with the encodedimage sequences 114 from storage 108 to produce an edited encodedsequence 118.

There are several formats currently available for encoding motionpictures, i.e., a temporal sequence of images, to produce the encodeddata 102. Some formats use intraframe compression, while others use bothinterframe and intraframe compression. Some of these formats arestandards and include, but are not limited to, the standards commonlyknown as MPEG-2 and H.264. Other formats may borrow concepts from or useparts of these standards. For example, a format known as HDV encodesprogressively scanned high-definition image sequences captured at a rateof 23.976 frames per second using MPEG-2 encoding. The captured imagesequences is encoded as an image sequence at a second image rate, e.g.,29.97 frames per second or 59.94 fields per second, with information inthe encoded image sequence indicative of images that are repeated whendecoded. Such information may include any metadata that indicatesrepetition of image information at the granularity of a field or frame.

In MPEG-2, this information is known as a “repeat first field flag,”defined in ISO/IEC 13818-2, Subpart D.7.4.1-6.3,10 (Picture codingextension). In particular, each picture in an encoded image sequence hasa “repeat first field flag.” How the repeat first field flag isinterpreted when decoded depends on two other values in the encodedimage sequence. First, a “progressive_frame” value for each pictureindicates whether two fields of a frame are interlaced (i.e., weresampled at different points in time), by being set to zero, orprogressive (i.e., were sampled at the same point in time or aretemporally coherent), by being set to one. Second, each encoded sequencealso has a flag (called “progressive_sequence”) indicating whether thesequence is progressive (set to one) or not (set to zero). The repeatfirst field flag cannot be set if the progressive sequence andprogressive frame values are both zero.

When the progressive sequence value is zero and the progressive framevalue is one, if the repeat first field flag is set for a picture in anencoded image sequence, then the repeat first field flag causes adecoder to repeat a field. The first field is repeated, which may beeither the top or bottom field depending on another flag that indicateswhether the top or bottom field is first.

When the progressive sequence value is one, and if the repeat firstfield flag is set for a picture in an encoded image sequence, then therepeat first field flag causes a decoder to generate two or three framesdepending on the value of the top field first flag.

For, example, if a sequence of images originally captured at 24/23.976frames per second were encoded using MPEG-2 as a 59.94 or 60 field persecond sequence, or as a 29.97 or 30 frame per second sequence, then the“repeat first field” flag would be set for at least some of the picturesin the encoded image sequence.

In H.264 several pieces of information indicate whether a field is to berepeated, as defined in ISO/TEC 14496-10, Subpart D.2.2 (in particular,a “pic_struct”). In particular, H.264 permits several pic_struct valueswhich indicate that a field or frame is to be repeated. A value of “5”indicates that a picture should be displayed as a top field first, thena bottom field, then a top field repeated. A value of “6” indicates thata picture should be displayed as a bottom field first, then a top field,then a bottom field repeated. A value of “7” indicates frame doubling,or that a picture should be displayed as a frame two timesconsecutively. A value of “8” indicates frame tripling, or that apicture should be displayed as a frame that is displayed three timesconsecutively.

For example, if a sequence of images originally captured at 24/23.976frames per second were encoded using H.264 as a 59.94 or 60 field persecond sequence, or as a 29.97 or 30 frame per second sequence, then the“pic_struct” values of 5, 6, 7 or 8 would be found in the encoded imagesequence.

The encoded data 102 also may include audio data associated with thevideo data. In some formats, such as MPEG-2, the audio data may bemultiplexed with the video data within the encoded data 102. The audiodata may be compressed or uncompressed.

To assist in editing a video program using the encoded image sequence,the encoded image sequence is subjected to a capture process 104. Inparticular, the information in the encoded image sequence indicative ofimages that are repeated when decoded may be cleared. For example, usingMPEG-2, the repeat first field flags would be cleared i.e., reset tozero. Using H.264, “pic_struct” values of 5, 6, 7 or 8 would be clearedto either 0 (such as for 24/23.976 frame per second material) or 1 or 2(such as for 48/47.952 field per second material).

Further, image index information for the encoded image sequence may begenerated. This image index information is used to map a temporalposition of an image in a decoded image sequence to a position ofcorresponding data in the encoded image sequence. Temporal positionsused with the image index information correspond to the first imagerate. The image index information may include a known amount of data foreach image if the encoding process produces the same amount of encodeddata for each encoded image. If the encoding process produces adifferent amount of data for each encoded image, then an image index iscreated and used.

In some formats of encoded video data, such as MPEG-2, the temporalorder of the encoded images is different from the order in which theencoded data appears in the encoded bitstream. Thus the image index mapsthe temporal order of images to the bitstream order of encoded data forthe images and to the position of the encoded data in the encodedbitstream. Such an image index is described in U.S. Pat. Nos. 6,337,880,6,584,152 and 6,792,433.

The encoded image sequence may already have an original image index thatmaps a temporal position of an image in a decoded image sequence to aposition of corresponding data in the encoded image sequence, whereinthe temporal positions used in the image index correspond to the secondimage rate. In this case, the image index takes into account therepeated images. If the information indicative of the repeated images iscleared from the encoded image sequence, a new image index is created.The new image index may be created by processing the encoded imagesequence. Alternatively the new image index may be created by convertingthe original image index into an image index which maps a temporalposition of an image in a decoded image sequence to a position ofcorresponding data in the encoded image sequence, wherein the temporalpositions used in the image index correspond to the first image rate.

The encoded image sequence with cleared information about repeatedimages and its image index information may be stored in a separate datafile, such as a data file in the material exchange format (MXF), whichis the subject of the standardization process of the Society of MotionPicture and Television Engineers (SMPTE), and is defined in documentsincluding SMPTE S377M through 394M, with SMPTE Engineering GuidelinesEG41 and 42. In addition, any audio data (if present) may be separatedfrom the video data and stored in a separate file.

Thus, the processed encoded data 106 includes separate video and(optional) audio files. The processed encoded data is stored in storage108. Storage 108 may have a number of different forms. It may be storagein a personal computer, storage within a camera, or shared storageaccessed by multiple computers over a network. The storage may be fixedwithin a device or may be removable from a device to which it isattached. In general the storage should be random-access storage, andmay be rewriteable.

The capture process 104 may be part of live recording or may be part ofprocessing of prerecorded information. For example, if the captureprocess 104 and storage 108 are implemented by either software orcircuitry in the housing of a video camera, the processed encoded data106 may be generated at the time of live recording of the encoded data102. In such an implementation, the encoded data 102 may be a standardrecording format for a camera and the processed encoded data 108provides a format that is more suitable for editing. As another example,the capture process 104 may be implemented by either software orcircuitry associated with an editing system to generate the processedencoded data 106 as part of an import or preparation step prior toediting.

Turning now to FIG. 2, the additional processing of any audio dataassociated with the video data will now be described. In general, asnoted above, any audio data (if present) may be separated from the videodata and stored in a separate file. If this audio data is multiplexedwith the video data within the received encoded data 200, the encodeddata is demultiplexed 202 to separate the audio data 204 and the videodata 206. If this audio data is compressed, it may be decompressed 208.The uncompressed audio data 210 then may be stored in a separate file.The editing system 212 then accesses the separate video data 206 anduncompressed audio data 210. The export process 216 applied to anyedited sequence 214 uses the separate video data 206 and uncompressedaudio data 210. The audio data may be compressed and multiplexed withthe encoded video data to produce a multiplexed output stream 220.

Turning again to FIG. 1, the editing of the processed encoded data 106will now be described in more detail. Editing a video program using suchaudio and video data involves defining a sequence 112 of clips thatreference source encoded image sequences using edit points. Each cliphas a start and stop point (which may be inferred from a duration) inits corresponding source and a position for the clip in the edited videoprogram. The temporal resolution of these edit points corresponds to thefirst image rate. Generally, the editing system 110 permits an editor tospecify these edit points at any frame boundary at the resolution of thefirst image rate. The information in any source encoded image sequenceindicative of images that are repeated when decoded may be ignored bythe editor or may have already been cleared by the capture process.

Playback of an edited sequence involves random access into the encodedimage sequence. The image index information, as described above,provides this capability. In particular, the image index information isused to map a temporal position of an image in a decoded image sequenceto a position of corresponding data in the encoded image sequence.Temporal positions used in an image index correspond to the first imagerate. The edited video program may be played back at the first imagerate. To playback the edited video program at another image rate, suchas the second image rate, images may be repeated. Whether an image isrepeated depends on a cadence that corresponds to a difference betweenthe first image rate and the other image rate, but is independent of anyinformation in the source encoded image sequences that may indicative ofimages that are repeated when decoded.

An edited video program is output as an encoded image sequence, usingsource encoded image sequences referenced by the sequence of clips. Theencoded image sequence is constructed according to the edited sequenceof clips, using the source encoded image sequences. In particular, anyinformation in the source encoded image sequences, used in the sequenceof clips, indicative of images that are repeated when decoded iscleared. In the output encoded image sequence, information indicative ofimages that are repeated when decoded is set according to a cadenceassociated with a difference between the first image rate and the secondimage rate. In some cases, the result of editing involves applying aneffect to a source encoded image sequence. In such a case, the encodedimage sequence needs to be decoded, modified according to the effect,and re-encoded.

Referring now to FIGS. 3 and 4, the encoding process will now bedescribed in more detail. FIG. 3 illustrates a portion of an editedsequence 300. This portion of an editing sequence includes a first clip306 and a second clip 308, and a transition 310 from the first clip tothe second clip. The source encoded image sequences in each clip alsowill include one or more I-frames 312. Any portion of the editedsequence between two I-frames of its source material that is completeand that does not require any rendering (for example, due to an effect)can be used in the output encoded data directly in its already encodedform. These portions are called unrendered portions 302. Any portion ofthe edited sequence between two I-frames that requires rendering (forexample to render a transition) is decoded, rendered and thenre-encoded. These portions are called rendered portions 304. Thus, theedited sequence can be considered to include unrendered portions 302 andrendered portions 304.

Referring now to FIG. 4, the encoding process begins by identifying(400) all unrendered portions and rendered portions, The renderedportions are rendered and encoded (401). For unrendered portions, theencoder clears (402) any information in the source encoded imagesequences indicative of images that are repeated when decoded, if thatinformation was not previously cleared. The encoded rendered portionsand the source encoded image sequences for the unrendered portions arethen stitched (404) together into an encoded sequence. When stitchingthese encoded portions together, the state information in the headersthat is used for decoding is made internally consistent. Next,information indicative of images that are repeated when decoded is thenset (406) in the encoded sequence according to a cadence. The cadencecorresponds to the difference between the first image rate (at which thesource image sequence was originally captured) and the desired playbackrate to be used when decoding the encoded edited sequence. The encodedvideo data then may be packaged (408) with other information. Forexample, the video data may be multiplexed with audio data and stored ina file.

The various components of the system described herein may be implementedas a computer program using a general-purpose computer system. Thecapture process and related storage also may be found in a camera or ina field capture device connected to a camera to permit the captureprocess to be performed during live recording. Such a computer systemtypically includes a main unit connected to both an output device thatdisplays information to a user and an input device that receives inputfrom a user. The main unit generally includes a processor connected to amemory system via an interconnection mechanism. The input device andoutput device also are connected to the processor and memory system viathe interconnection mechanism.

One or more output devices may be connected to the computer system.Example output devices include, but are not limited to, a cathode raytube (CRT) display, liquid crystal displays (LCD) and other video outputdevices, printers, communication devices such as a modem, and storagedevices such as disk or tape. One or more input devices may be connectedto the computer system. Example input devices include, but are notlimited to, a keyboard, keypad, track ball, mouse, pen and tablet,communication device, and data input devices. The invention is notlimited to the particular input or output devices used in combinationwith the computer system or to those described herein.

The computer system may be a general purpose computer system which isprogrammable using a computer programming language, a scripting languageor even assembly language. The computer system may also be speciallyprogrammed, special purpose hardware. In a general-purpose computersystem, the processor is typically a commercially available processor.The general-purpose computer also typically has an operating system,which controls the execution of other computer programs and providesscheduling, debugging, input/output control, accounting, compilation,storage assignment, data management and memory management, andcommunication control and related services.

A memory system typically includes a computer readable medium. Themedium may be volatile or nonvolatile, writeable or nonwriteable, and/orrewriteable or not rewriteable. A memory system stores data typically inbinary form. Such data may define an application program to be executedby the microprocessor, or information stored on the disk to be processedby the application program. The invention is not limited to a particularmemory system.

A system such as described herein may be implemented in software orhardware or firmware, or a combination of the three. The variouselements of the system, either individually or in combination may beimplemented as one or more computer program products in which computerprogram instructions are stored on a computer readable medium forexecution by a computer. Various steps of a process may be performed bya computer executing such computer program instructions. The computersystem may be a multiprocessor computer system or may include multiplecomputers connected over a computer network. The components shown inFIG. 1 may be separate modules of a computer program, or may be separatecomputer programs, which may be operable on separate computers. The dataproduced by these components may be stored in a memory system ortransmitted between computer systems.

Having now described an example embodiment, it should be apparent tothose skilled in the art that the foregoing is merely illustrative andnot limiting, having been presented by way of example only. Numerousmodifications and other embodiments are within the scope of one ofordinary skill in the art and are contemplated as falling within thescope of the invention.

1. A method for editing encoded data including an image sequencecaptured at a first image rate and encoded as an image sequence having asecond image rate with information in the encoded image sequenceindicative of images that are repeated when decoded, the methodcomprising: receiving image index information for the encoded imagesequence that is used to map a temporal position of an image in adecoded image sequence to a position of corresponding data in theencoded image sequence; permitting an editor to create a sequence ofsegments of encoded image sequences at a temporal resolutioncorresponding to the first image rate; and during playback of theencoded image sequence, decoding the encoded image sequence, using theimage index information, to produce a decoded image sequence at thefirst image rate by not repeating images.
 2. The method of claim 1,wherein the temporal positions used with the image index informationcorrespond to the first image rate.
 3. The method of claim 1, whereindecoding includes ignoring the information in the encoded imagesequences indicative of images that are repeated when decoded.
 4. Themethod of claim 2, further comprising, prior to decoding, clearing theinformation in the encoded image sequences indicative of images that arerepeated when decoded.
 5. The method of claim 4, further comprisingcreating the image index information.
 6. The method of claim 5, whereincreating the image index information comprises: receiving an originalimage index of the encoded image sequence that maps a temporal positionof an image in the image sequence to a position of corresponding data inthe encoded image sequence, wherein the temporal positions used in theimage index correspond to the second image rate; and converting theoriginal image index into a new image index for the encoded imagesequence that maps a temporal position of an image in the image sequenceto a position of corresponding data in the encoded image sequence,wherein the temporal positions used in the new image index correspond tothe first image rate.
 7. The method of claim 1, wherein the temporalpositions used with the image index information correspond to the secondimage rate.
 8. The method of claim 7, wherein decoding includes ignoringthe information in the encoded image sequences indicative of images arerepeated when decoded.
 9. The method of claim 7, further comprising,prior to decoding, clearing the information in the encoded imagesequences indicative of images that are repeated when decoded.
 10. Themethod of claim 1, wherein the encoded data includes audio dataassociated with the encoded image sequence, the method furthercomprising: separating the encoded image sequence and the audio datafrom the encoded data into separate data files.
 11. The method of claim10, wherein the audio data and the encoded image sequences aremultiplexed together in the encoded data and wherein separating includesdemultiplexing the audio data from the encoded image sequence.
 12. Themethod of claim 1, wherein the information in the encoded imagesequences indicative of images that are repeated when decoded includes arepeat field flag associated with encoded data for each image that is tobe repeated when decoded.
 13. The method of claims 12, wherein theencoded image sequence is encoded according to the MPEG-2 standard. 14.The method of claim 1, wherein the encoded image sequence is encodedaccording to the H.264 standard.
 15. A computer program product,comprising: a computer readable medium; computer program instructionsstored on the computer readable medium that, when processed by acomputer, instruct the computer to perform a method for editing encodeddata including an image sequence captured at a first image rate andencoded as an image sequence having a second image rate with informationin the encoded image sequence indicative of images that are repeatedwhen decoded, the method comprising: receiving image index informationfor the encoded image sequence that is used to map a temporal positionof an image in a decoded image sequence to a position of correspondingdata in the encoded image sequence; permitting an editor to create asequence of segments of encoded image sequences at a temporal resolutioncorresponding to the first image rate; and decoding the encoded imagesequence, during playback of the encoded image sequence, using the imageindex information, to produce a decoded image sequence at the firstimage rate by not repeating images.
 16. A computer system for editingencoded data including an image sequence captured at a first image rateand encoded as an image sequence having a second image rate withinformation in the encoded image sequence indicative of images that arerepeated when decoded, the computer system comprising: a memory forreceiving image index information for the encoded image sequence that isused to map a temporal position of an image in a decoded image sequenceto a position of corresponding data in the encoded image sequence; aninput for receiving instructions from an editor to create a sequence ofsegments of encoded image sequences at a temporal resolutioncorresponding to the first image rate; and a processor programmed todecode the encoded image sequence, during playback of the encoded imagesequence, using the image index information, to produce a decoded imagesequence at the first image rate by not repeating images.
 17. A methodfor exporting an edited image sequence having a first image rate as anencoded image sequence having a second image rate different from thefirst image rate, the method comprising: receiving data describing anedited sequence of clips that reference source encoded image sequencesusing edit points at a temporal resolution corresponding to the firstimage rate; constructing the encoded image sequence according to theedited sequence of clips and using the source encoded image sequences,including: clearing any information in the source encoded imagesequences, used in the sequence of clips, indicative of images that arerepeated when decoded; and setting, in the encoded image sequence,information indicative of images that are repeated when decodedaccording to a cadence associated with the difference between the firstimage rate and the second image rate.
 18. The method of claim 17,wherein the information in the encoded image sequence indicative ofimages that are repeated when decoded includes a repeat field flagassociated with each image that is repeated when decoded.
 19. The methodof claim 18, wherein the encoded image sequence is encoded according tothe MPEG-2 standard.
 20. The method of claim 19, wherein the encodedimage sequence is encoded according to the H.264 standard.
 21. Themethod of claim 17, wherein constructing further comprises: identifyingrendered portions of the edited sequence; rendering and encoding therendered portions of the edited sequence; setting information, in theencoded rendered portions in the encoded edited sequence, indicative ofimages that are repeated when decoded according to a cadence associatedwith the difference between the first image rate and the second imagerate.
 22. The method of claim 17, wherein constructing furthercomprises: identifying rendered portions and unrendered portions of theedited sequence; for each unrendered portion, inserting data from acorresponding source encoded image sequence into the encoded editedsequence; and for each rendered portion, rendering and encoding therendered portions of the edited sequence; and inserting data the encodedrendered portions into the encoded image sequence.
 23. Acomputer-implemented method for processing data including an imagesequence captured at a first image rate and encoded as an encoded imagesequence having a second image rate with information in the encodedimage sequence indicative of images that are repeated when decoded, themethod comprising: receiving the encoded image sequence; receiving imageindex information for the encoded image sequence that is used to map atemporal position of an image in a decoded image sequence to a positionof corresponding data in the encoded image sequence wherein the temporalpositions used with the image index information correspond to the firstimage rate; permitting an editor to create a sequence of segments ofencoded image sequences at a temporal resolution corresponding to thefirst image rate; and decoding the encoded image sequence, duringplayback of the encoded image sequence, using the image indexinformation, to produce a decoded image sequence at the first image rateby not repeating images.
 24. A computer-implemented method forprocessing data including an image sequence captured at a first imagerate and encoded as an image sequence having a second image rate withinformation in the encoded image sequence indicative of images that arerepeated when decoded, the method comprising: receiving the encodedimage sequence; clearing all information in the encoded image sequenceindicative of images that are repeated when decoded; receiving imageindex information for the encoded image sequence that is used to map atemporal position of an image in a decoded image sequence to a positionof corresponding data in the encoded image sequence wherein the temporalpositions used with the image index information correspond to the firstimage rate; permitting an editor to create a sequence of segments ofencoded image sequences at a temporal resolution corresponding to thefirst image rate; and decoding the encoded image sequence, duringplayback of the encoded image sequence, using the image indexinformation, to produce a decoded image sequence at a second image ratedifferent from the first image rate by repeating fields according to acadenced based on the difference between the first image rate and thesecond image rate.
 25. A computer-implemented method for editing encodeddata including an image sequence captured at a first image rate andencoded as an image sequence having a second image rate different fromthe first image rate, with information in the encoded image sequenceindicative of images that are repeated when decoded, to produce anencoded edited sequence, the method comprising: receiving image indexinformation for the encoded image sequence that is used to map atemporal position of an image in a decoded image sequence to a positionof corresponding data in the encoded image sequence, wherein thetemporal positions used with the image index information correspond tothe first image rate; permitting an editor to create an edited sequenceof clips that reference source encoded image sequences using edit pointsat a temporal resolution corresponding to the first image rate; andconstructing the encoded edited sequence according to the editedsequence of clips and using the source encoded image sequences,including: clearing any information in the source encoded imagesequences, used in the sequence of clips, indicative of images that arerepeated when decoded; and setting, in the encoded image sequence,information indicative of images that are repeated when decodedaccording to a cadence associated with the difference between the firstimage rate and the second image rate.